The Siemens 3RU2126-4AB0-ZX95 is a SIRIUS thermal overload relay — size S0, CLASS 10 trip curve — designed for motor protection in control panels. It mounts directly onto the contactor (fastening method: contactor mounting) and uses a thermal bimetallic release to track motor heating. Rated voltage is 690 V; at 400 V it handles motor loads up to 7.5 kW.
The auxiliary contact ratings tell you what the signal side can switch: 2 A at 24 V, 2 A at 230 V, 1 A at 400 V, and 3 A at 120 V — these cover typical PLC input or relay coil loads. The main circuit is screw-type terminals (M4) accepting 2x 0.5–1.5 mm² or 2x 0.75–2.5 mm² solid/stranded. Temperature compensation is active from -40 °C to +60 °C, so the trip curve stays consistent across the panel's ambient range. Mounting position is any, which helps when the enclosure forces a horizontal or upside-down layout. Power dissipation per pole is 2.7 W — factor that into the panel heat budget.
The screwdriver tip required is Pozidriv PZ2, shaft diameter 5–6 mm. The integrated auxiliary switch eliminates one extra wiring step; just confirm the NC/NO configuration matches your PLC input logic.